Much work has been devoted to the recovery of various nylon fibers such as nylon 6 and nylon 6,6 from carpets because of the value of such polymers. The nylon-containing carpets, generally contain three components, for example from about 40 to about 60 weight percent and generally approximately about 50 weight percent of nylon 6 fiber or alternatively, nylon 6,6 fiber, and generally from about 20 to about 30 and approximately about 25 percent by weight of the carpeting is a polyolefin, such as polypropylene backing generally in the form of a horizontal weave intertwined with the upright or vertical nylon fibers as well as any polyolefin fibers. The remaining amount of from about 20 to about 30 and approximately 25 percent by weight of the carpet composition is an adhesive, such as, but not limited to, a latex adhesive backing or glue that is generally a mixture of rubber such as styrene-butadiene rubber and an inexpensive non-water soluble filler such as calcium carbonate (CaCO3) powder. CaCO3 filled PVC is also used. As known to the art, heat rollers applied to the backing of the carpet generally set or cure the rubber and thus forms a rubber backing.
Polypropylene is incompatible or immiscible with nylon. It also has inferior physical properties to nylon such as much lower melt temperature and substantially lower strength. Congealed droplets of polypropylene serve as crack initiation points, lowering the overall strength of nylon product. The droplets on the surface of a molded part can give poor appearance. The “polymer blooming” of polypropylene can detract from paint and decal adherence. To combat this, expensive ingredients known as compatiblizers can be added with a certain degree of mitigation.
U.S. Pat. No. 7,784,719 granted Aug. 31, 2010, to Wellman Plastics Recycling, LLC relates to methods of recovering primary construction materials from whole carpet. A negative result is that the utilization of a dry size reduction process inherently involves high frictional contact that softens the polypropylene such that it attaches to itself and to nylon fibers resulting in a fiber combination that neither sinks nor floats. The resulting reclaimed nylon can contain detectable amounts of polypropylene therein.
U.S. Publication 2013/0174517 published Jul. 11, 2013, to Environmental Recycled Carpet Systems, LLC relates to a carpet recycling method wherein a toroidal flow pulper shears a carpet in the presence of a liquid to form a slurry of fibrous carpet materials and latex/calcium carbonate solids. After drying, a first output comprising dried separated fibrous carpet materials is produced, and a second output comprising dried latex/calcium carbonate solids is produced. A negative aspect of this application is that it does not adequately reduce the fiber length for efficient separation. Additionally, this process can obtain polypropylene fibers that melt due to the high shear utilized in dry granulation resulting in a high level of contamination between the carpet fiber and backing.
U.S. Publication 2014/0251545 published Sep. 11, 2014, to Burich and Murdock relates to a process and method for recycling carpet wherein desired carpet face fibers are reportedly liberated and separated from the carpet backing. The process reportedly eliminates face fiber shearing. The secondary layer of the carpet backing is then removed either manually or mechanically. Then, the bottom of the primary backing layer of the carpet with the bottom of the face fiber “U's” exposed, is mechanically grip-abraded by a rubber material. The grip-abrasion of the rubber or rubber-like material across the bottom of the primary carpet backing layer loosens the glue and grips and pulls the face fiber from the primary backing reportedly without destructing primary or secondary backing and allows the backing material to be recycled. A dry process is thus utilized with its inherent negative aspect of softening polypropylene. Fiber shortening is not effectively achieved.